For a device that supports both power supplying by a rechargeable battery and direct power supplying by a power supply (for example, a mobile electronic device such as a mobile phone and a portable instrument), when the device with the rechargeable battery is connected to a power supply (for example, a universal serial bus USB or power adapter), the power supply charges the battery and supplies power to the system simultaneously through a charging and power supplying circuit. With increase of the system power consumption of the device, the efficiencies of battery charging and system power supplying become more and more important. Specifically, the higher the efficiencies of system power supplying and battery charging are, the smaller the loss in the system power supplying and battery charging is, and the less the heat a chip produces. In this way, the service life of the device is prolonged, and the difficulty of designing a heat dissipation structure of a board-level system is reduced. In addition, the improved efficiencies of battery charging and system power supplying also help to prolong the service life of the battery.
Currently, the following three types of common charging and power supplying circuits are mainly used.
In a charging and power supplying circuit shown in FIG. 1, a power supply (USB or power adapter) 11 charges a battery and supplies power to a system simultaneously through a charging control chip (not shown in FIG. 1), and the system 14 is directly connected to the battery 13.
With such a charging and power supplying circuit, once the battery 13 is installed in the device, the system 14 is powered only by the battery 13, and the battery 13 discharges while being charged. As a result, the charging time of the battery 13 is prolonged and the charging is repeated, which leads to low efficiency of battery charging and reduces the service life of the battery 13. In addition, in this solution, if a charger 12 is a linear charger, both the charging efficiency and the power supplying efficiency are very low.
FIG. 2 shows a currently prevalent charging and power supplying circuit. In the circuit, a power supply (USB or power adapter) 21 charges a battery 23 and supplies power to a system 24 respectively through a charging control chip (not shown in FIG. 2). An end of an LDO (Low Dropout regulator, low dropout regulator)/switch 25 is connected to the power supply, and another end is connected to a first end of a linear charger 22 and to the system 24. A second end of the linear charger 22 is connected to the battery 23.
In this solution, the linear charger 22 is adopted for charging the battery 23, so both the charging efficiency and the power supplying efficiency are very low.
FIG. 3 shows a charging and power supplying circuit that is mainly recommended in the industry currently. As shown in FIG. 3, a power supply (USB or power adapter) 31 is connected to an input end of a BUCK circuit (buck converter circuit) 35, and an output end of the BUCK circuit 35 is connected to a system 34 and a source of a system load switch 32 respectively. A drain of the system load switch 32 is connected to a battery 33. In this solution, a switch circuit is adopted to provide a total current for the charging tributary and the system power supplying tributary, and the system load switch 32 is mainly utilized to perform linear control on the charging for the battery 33. Through loop control, the voltage on the system 34 follows the voltage of the battery 33 to improve the charging efficiency.
The defects lie in that, because the switch circuit supplies power to the system, the efficiency of the switch circuit is the efficiency of supplying power to the system 34; and the range of variation of the load is wide so the average efficiency is low. The efficiency of charging the battery 33 depends on a product of the efficiency of the switch circuit and the efficiency of the system load switch 32. Because the efficiency of the load switch 32 is less than 1, the charging efficiency is always lower than the efficiency of the switch circuit.
It can be seen that, charging technical solutions in the prior art can hardly overcome the low efficiencies of battery charging and system power supplying.